In recent years, there is an increasing need for lightening weight in various fields such as electrical and electronic equipments, automobiles, medical equipments, aircrafts, building materials, and general industrial parts, and housings or parts thereof need to be lightweight and to have high rigidity. As the housings or parts having a thin thickness and high rigidity, there have been used a shaped product in which a rolled plate of an aluminum alloy or a magnesium alloy is pressed, a shaped product obtained using a dicasting molding, a shaped product obtained by injection-molding a fiber-reinforced composite material filled with glass fibers or carbon fibers, or a shaped product obtained by integrally injection-molding a fiber-reinforced composite material plate with a thermoplastic resin.
The aluminum alloy or the magnesium alloy has excellent strength or rigidity, but since there is a limitation of shape formability, it is difficult to mold a complicate shape therewith only. Further, there is a problem in that a metal member (particularly, a magnesium alloy) has low corrosion resistance, and there is a problem in that a surface is corroded by moisture in the atmosphere or moisture or salts contained in sweat of a user to cause bad appearance of the member.
Patent Document 1 suggests a method for manufacturing a housing, including a coating step of coating the entire member made of a magnesium alloy with a resin layer, and a molding step of integrally molding the member and such a resin part. In this method, it is possible to form a complicate shape and give corrosion resistance, but a process is complicated. Further, although an aluminum alloy or a magnesium alloy, and a resin have specific strength higher than iron, but specific strength thereof is lower than a fiber-reinforced composite material to be described below. Therefore, there is a limitation in achieving lightening weight.
Since the fiber-reinforced composite material has specific strength, excellent specific rigidity, and excellent corrosion resistance, the fiber-reinforced composite material has been used in a wide field for the purpose described above. In particular, the shaped product made of the fiber-reinforced composite material filled with the glass fibers or the carbon fibers has been widely used due to high flexibility in shape and high productivity. However, since a length of the fiber included in a shaped article is shortish, the shaped product has still a problem in use requiring high strength or rigidity.
Meanwhile, due to excellent specific strength and specific rigidity, the fiber-reinforced composite material reinforced by using a continuous fiber has been primarily used in use requiring high strength or rigidity. However, since the aforementioned fiber-reinforced composite material is low flexibility in shape in comparison to a resin, or a fiber-reinforced composite material through injection-molding, it is difficult to mold a complicate shape with a simple substance. Furthermore, there is a problem in that since the fiber-reinforced composite material is manufactured by layering the reinforcing fibers in a woven fabric form in multiple layers, productivity is low. Patent Document 2 suggests a composite shaped product obtained by joining a resin member to an outer edge of a plate-shaped member made from a sheet including a reinforcing fiber, particularly, a continuous fiber. Accordingly, it is possible to implement a shaped product having a complicate shape. However, since the shaped product is manufactured through multiple processes, productivity may be not high. In addition, the fiber-reinforced composite material using the continuous fiber is typically obtained by heating and pressurizing, for two hours or more, a material, which is called a prepreg obtained by previously impregnating a thermosetting resin into a reinforcing fiber base material.
There has been recently suggested a RTM molding method in which after a reinforcing fiber base material into which a resin is not impregnated is set in a mold, a thermosetting resin is allowed to flow in the mold, and in this method, a molding time is remarkably reduced. However, even in the RTM molding method, since it takes a time of 10 minutes or more to mold one part, productivity is not improved.
For this reason, there has been noticed a fiber-reinforced composite material manufactured using a thermoplastic resin as a matrix instead of the conventional thermosetting resin (for example, Patent Document 3). However, the fiber-reinforced composite material manufactured using the thermoplastic resin as a matrix is now being studied and developed, and a technology for obtaining a shaped product having an excellent surface appearance and a quality endurable to practical use by molding the fiber-reinforced composite material has not been sufficiently established.